1. Field of the Invention
The present invention relates to a gearshift control apparatus for an automatic transmission wherein a skip downshift from a higher speed stage to a lower speed stage in a power-ON state is executed via a stage intermediate between the higher and lower speed stages. Here, each of a gearshift from the higher speed stage to the intermediate stage, and a gearshift from the intermediate stage to the lower speed stage is done through a clutch to-clutch operation based on releasing and engaging a plurality of clutches.
2. Description of the Prior Art
A power-ON skip downshift is executed when the driver of a motor vehicle has deeply pressed the accelerator pedal in order to attain a rapid acceleration.
The official gazette of Japanese Patent Application Laid-open No. 121362/1991 discloses a control technique wherein the power-ON skip downshift of, for example, the fourth speed stage.fwdarw.second speed stage of an automatic transmission is executed by clutch-to-clutch gearshifting. The gearshift control is performed via the intermediate stage (third speed stage) of the automatic transmission, and a command for the intermediate stage is canceled before this intermediate stage is completely achieved.
When the intermediate stage is involved in executing a skip gearshift, the r.p.m. or, rotational speed of a rotary member can be changed more smoothly and a gearshift shock can be alleviated.
On that occasion, the whole gearshifting period of time required till the completion of the skip gearshift can be shortened by applying the technique as disclosed in the above official gazette of Japanese Patent Application Laid-open No. 121362/1991.
The control technique in the prior art, however, uses a one-way clutch for achieving the engagement of the 1intermediate stage. That is, the prior-art technique has the problem that it cannot be simply applied to an automatic transmission of the type in which the engagement of the intermediate stage is achieved by the clutch-to-clutch operation. As is well known, when the one-way clutch is mounted anew, increases in weight and in cost are incurred correspondingly.